A luteolytic interaction between estradiol (E2) and PGF2 alpha as been demonstrated which is independent of the uterus. This ineraction could not be demonstrated in vitro with dispersed luteal cells since PGF2 alpha increased progesterone accumulation and estradiol was without effect in the absence or presence of PGF2 alpha. The objectives of the present experiments are to determine if the luteolytic sites of PGF2 alpha and estradiol action are on blood flow, at the luteal cell level or both. Primary cultures of bovine corpora lutea will be employed to evaluate effects of PGF2 alpha and E2 at the luteal cell level; since E2-induced luteolysis is slow to develop in vivo, a longer in vitro evaluation may be required. A longer in vitro incubation with PGF2 alpha may also be required since in vivo administration increased plasma progesterone before a fall in circulating progesterone concentrations was observed. To determine if membrane receptors for PGF2 alpha mediate the luteolytic effects observed with dispersed luteal cells, PGF2 alpha will be coupled to dextran to prevent entry into cells and correlated with changes in cAMP and progesterone synthesis. Effects of in vitro treatments with PGF2 alpha and E2 on luteal blood flow will also be evaluated by uptake of trypan blue administered just before removal of the corpus luteum. The in vitro response to LH and the presence of an inhibitor to LH binding will also be determined with these corpora lutea.